Switching mode power supplies are widely used due to high efficiencies and small sizes. In a typical switching mode power supply, a pulse width modulation (“PWM”) control scheme is commonly used. However, with traditional PWM control, the switching mode power supply generates pulses only according to an absolute COMP value.
FIG. 1 illustrates a schematic circuit of a prior art switching mode power supply 100. As shown in FIG. 1, the switching mode power supply 100 comprises a power stage 101 configured to receive an input voltage (VIN), and provides an output voltage (VOUT) based on a driving signal. A feedback circuit 102 provides a feedback signal derived from a load to an error amplifier 103 configured to receive the feedback signal and a voltage reference (VREF), and amplifies the difference between the feedback signal and the voltage reference to provide an error amplified signal, i.e., a COMP signal (VCMP). A controller (e.g., a PWM generator) 104 generates a PWM signal in response to the COMP signal and a current sense signal from the power stage. A driver 105 provides the driving signal to the power stage 101 in response to the PWM signal, so that the power stage 101 provides the desired output voltage (VOUT).
In the switching mode power supply 100, the PWM generator generates the PWM pulses according to an absolute COMP value. Even if the output voltage (VOUT) is going up, the PWM generator continuously generates PWM pulses as long as the COMP signal (VCMP) is high. This results in a ring back and worsens a transient performance of the switching mode power supply 100. So there is a need for switching mode power supplies with improved PWM control.